This invention is directed to an electronic control system that utilizes a variable load sense relief, variable working margins, and electronic torque limiting. The system includes an apparatus having sensors that detect pressure on opposite sides of a control valve that control hydraulic flow from a source to a hydraulic actuator. The sensors produce electrical signals indicating pressure. In response to the sensor signals, a controller produces an output signal which operates a proportional control valve to regulate pressure at a node of a hydraulic circuit.
Mechanisms that react to pressure at a node by varying pressure of the fluid being supplied to a main valve so that a controlled pressure level is achieved are known in the art. For one example of the state of the art, a mechanism uses pressure transducers and an Electronic Control Unit (ECU) to sense a load being applied to various machine functions. The ECU program monitors the pressure at several points in the circuit to optimize pump flow in relation to the speed demanded by the operator. Another example of the state of the art uses an electronic pressure control system having a proportional regulator that replaces a hydro-mechanical pressure limiter. The proportional relief valve acts on a pilot signal of a hydro-mechanical LS (load sense) regulator so that pump output pressure is proportional to a control current. Thus, the load sensing function is realized by an electronic control unit reading the instantaneous measurement of two pressure transducers, the first one on the pump outlet line and the second one on the valve LS port. An output current signal controls a proportional valve regulating the pump outlet pressure according to the instantaneous LS pressure. Yet another example of the state of the art uses embedded sensors to monitor pressure, displacement, speed, and temperature. The sensed data interacts with onboard electronics to help produce commanded functions including an integral proportional valve to position a pump's swashplate to produce flow and pressure outputs that control pump functions.
While these mechanisms have made improvements in the art, there are still problems associated with the load sensing system and the control of those systems that still exist. As an example, in applications where the pump is a long distance from the control spools, there can be difficulties associated with running high pressure hydraulic hoses from a control valve to a pump control. The length of the hoses cause response and stability problems for the entire system. Large overrunning loads, high inertia, or functions where the response is highly similar to the response of the pump can result in unstable operation.
To improve upon these problems use of electrical wires and a micro controller to replicate a load sense signal to a traditional pressure compensated load sense controlled pump would be beneficial. By electronically replicating the load sense signal at the pump the hydraulic load sense line may be removed which reduces cost. The addition of software can smooth circuit operation and eliminate previous instabilities inherent with traditional load sense systems. Also, by replacing the hydraulic signal with electrical lines and software permits pressure to be shifted from one direction to the other which provides a real variable working margin opportunity. Further, by adding an angle sensor to the system allows for a full variable electronic torque control to the system that further expands the capabilities of an open circuit variable axial piston pump.
Therefore, an objective of the present invention is to provide a load sensing control system that smooths circuit operation and eliminate instabilities inherent in traditional load sense systems.
Another objective of the present invention is to provide a load sensing control system that provides a full variable working margin.
A still further objective of the present invention is to provide a load sensing control system that removes a hydraulic load sensor line and reduce cost.
These objectives are merely a few of the objectives of the present invention and other objectives will be apparent to those of ordinary skill in the art based upon the following written description and drawings.